One-piece golf ball

ABSTRACT

The present invention provides a one-piece golf ball which retains whiteness without being tinged with yellow and is excellent in durability. The golf ball of the present invention comprises a golf ball body obtained by vulcanizing a rubber composition and a clear paint film coating the golf ball body, wherein a component serving as a pigment of the rubber composition consists of  
     1 to 7 parts of titanium oxide; and  
     0.05 to 0.2 part of a blue pigment with respect to 100 parts of a base rubber by mass(weight).

BACKGROUND OF THE INVENTION

[0001] 1. Filed of the Invention

[0002] The present invention relates to a one-piece golf ball comprising a golf ball body obtained by vulcanizing a rubber composition and a clear paint film coating the golf ball body, more particularly to a one-piece golf ball which has an excellent weather resistance, and is not tinged with yellow and retains white tone with times.

[0003] 2. Description of the Related Art

[0004] In a conventional one-piece golf ball, a clear paint was coated onto a white enamel paint to impart a bright whiteness to the surface of the golf ball. However, most of the one-piece golf balls were used in the golf ball shooting range, and thus so many shots caused the problems such as peeling of a white paint film and an adhesion of white paint to the club surface. Further, since there is a difference in the color tone between the golf ball body and a white paint film, when the white paint film is peeled, the peeled portion of the golf ball becomes conspicuous and causes the deterioration of the appearance.

[0005] In view of this problem, a one-piece golf ball where a clear paint is coated directly onto the surface of the golf ball body without coating a white enamel paint has been developed and used. However, this golf ball has inferior whiteness to the golf ball where the white enamel paint is coated. Japanese unexamined patent application H07-51403 has disclosed a method to impart whiteness to the golf ball body. In this method, a blue pigment and a violet pigment as well as titanium oxide are added in a proper amount into the rubber composition to obtain a golf ball which exhibits the white tone, although only the clear paint film is coating the golf ball body.

[0006] Since the golf balls have been used for several years in the golf shooting range, it is required for the golf ball to retain the white appearance for several years and have durability against many shots with the club. Although a conventional golf ball has a white color shortly after its production, the golf ball is getting tinged with yellow while being used for a long time. In Japanese unexamined patent application H07-51403, it is not suggested to retain the whiteness for a long time described above. Further, the large amount of titanium oxide which is used to impart whiteness causes to lower the durability of the golf ball body.

SUMMARY OF THE INVENTION

[0007] The present invention has been achieved in view of the above problems. It is an object of the present invention to provide a golf ball which appears white for a long term as well as initially and also exhibits an excellent durability.

[0008] The present invention provides a one-piece golf ball comprising a golf ball body obtained by vulcanizing a rubber composition and a clear paint film coating the golf ball body, wherein a component serving as a pigment of the rubber composition consists of

[0009] 1 to 7 parts of titanium oxide; and

[0010] 0.05 to 0.2 part of blue pigment with respect to 100 parts of a base rubber by mass(weight).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The golf ball of the present invention is a one-piece golf ball comprising a golf ball body obtained by vulcanizing a rubber composition with a peroxide, optionally the rubber composition containing a co-crosslinking, and a clear paint film coating the golf ball body, wherein a component serving as a pigment of the rubber composition consists of

[0012] 1 to 7 parts of titanium oxide; and

[0013] 0.05 to 0.2 part of blue pigment with respect to 100 parts of a base rubber by mass(weight). Each component used in the present invention will be described below.

[0014] The base rubber contained in the rubber composition includes, but is not limited to, butadiene rubber (BR), ethylene-propylene-diene terpolymer (EPDM), isoprene rubber (IR), isobutylene-isoprene rubber (IIR), natural rubber (NR), acrylonitrile butadiene rubber (NBR), and styrene butadiene rubber (SBR). Each of these rubbers can be used individually or in combination of at least two of them. Among them, the base rubber preferably comprises the butadiene rubber as a major component. More preferably, the base rubber comprises 50% or more by mass of the butadiene rubber. Further, the butadiene rubber is preferably a high cis-polybutadiene in which the content of cis-1,4-bond is not less than 90%. An example of the high cis-polybutadiene rubber is BR-11 available from Nihon Gosei Rubber.

[0015] The co-crosslinking agent may be used in the present invention. The co-crosslinking agent includes α,β-unsaturated carboxylic acids such as acrylic acid or methacrylic acid, and metal salts thereof. Examples of them are zinc acrylic acid and zinc methacrylic acid.

[0016] The amount of the unsaturated carboxylic acid and/or a metal salt thereof is preferably 15 to 40 parts and more preferably 18 to 38 parts, with respect to 100 parts of the base rubber by mass. If the amount of the unsaturated carboxylic acid and/or a metal salt thereof is less than 15 parts, the resulting ball body becomes excessively soft and largely deforms when a shot is made, and an adhesion of the clear paint film may be deteriorated. In contrast, an amount of the unsaturated carboxylic acid exceeding 40 parts by mass causes an excessively hard shot feeling.

[0017] The peroxide may be used for vulcanizing the rubber composition. The peroxide includes, for example, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Dicumyl peroxide is typically preferred. The amount of the peroxide is preferably 0.3 to 5.0 parts, and more preferably 0.5 to 3.0 parts, with respect to 100 parts of the base rubber by mass.

[0018] In the present invention, as a component serving as a pigment of the rubber composition, titanium oxide and a blue pigment are used. The titanium oxide serves as a white pigment, and the blue pigment imparts brightness to the golf ball body. When only the titanium oxide as a white pigment is used, the obtained golf ball does not give the bright whiteness. Further, the golf ball cannot retain the white tone because the base rubber and the clear paint film are getting tinged with yellow as they are deteriorating with time. Therefore, in the present invention, a blue pigment is used as a component serving as a pigment of the rubber composition to prevent the golf ball from being tinged with yellow because of the deterioration proceeding with time. Since blue is a complementary color of yellow, if the blue tone of the golf ball is enhanced, the golf ball can retain the whiteness even when the base rubber and the clear paint film are getting tinged with yellow with time.

[0019] In the present invention, the component serving as a pigment consists of titanium oxide and a blue pigment, because the desired bright whiteness is not obtained when the other color pigments are used in combination.

[0020] The amount of titanium oxide added is not less than 1 part, preferably not less than 2 parts, and not more than 7 parts, preferably not more than 5 parts with respect to 100 parts of the base rubber by mass(weight). If the amount is less than 1 part, the sufficient whiteness is not obtained, with the result that the obtained golf ball gives the transparent impression. If the amount is larger than 7 parts, the durability of the obtained golf ball is lowered. Therefore, in the present invention, the amount of titanium oxide added is limited to the relatively lower range of 1 to 7 parts by mass, thereby imparting the durability to the golf ball.

[0021] The amount of the blue pigment added is not less than 0.05 part, preferably not less than 0.10 part, and not more than 0.2 part, preferably not more than 0.15 part with respect to 100 parts of the base rubber by mass. If the amount of the blue pigment is less than 0.05, the blue tone of the golf ball body becomes too weak, thus it is not impossible to retain the white tone when the rubber composition and the clear paint film get tinged with yellow with time. If the amount is larger than 0.2 part, the initial blue tone is too intensive. According to the present invention, use of the blue pigment in a larger amount than the amount for the conventional golf ball enables to prevent the golf ball from being tinged with transparent even if the amount of titanium oxide is suppressed to the lower range in order to improve the durability. The blue pigment includes, without limitation, for example, ultramarine blue pigment, cobalt blue pigment, fast sky blue pigment, copper phthalocyanine blue pigment, prussian blue and the like.

[0022] The initial appearance of the golf ball of the invention preferably has the color tone which satisfies −16≦b≦−8 specified by Lab color specification at the initial state. In the present invention, the term “initial” means “the state of the golf ball shortly after the golf ball is produced”. If the initial b value of the color tone is less than −16, the blue tone is too intensive, and if the initial b value is more than −8, the whiteness is deteriorated when yellowed with times.

[0023] The “Lab color specification”, as used herein, is a color specification method prescribed by JIS-Z-8701 or JIS-Z-8728. A Lab color difference measured is determined by converting tristimulus values X, Y and Z as follows. In the measurement, there is used a color difference meter named “CR-221” manufactured by MINOLTA CO. in which a tristimulus values direct measuring method is adopted.

L=116(Y/Y _(N))^(1/3)−16

a=500[(X/X _(N))^(1/3)−(Y/Y _(N))^(1/3)]

b=200[(Y/Y _(N))^(1/3)−(Z/Z _(N))^(1/3)]

[0024] where X_(N), Y_(N) and Z_(N) are tristimulus values in the XYZ coordinate system of a perfect diffuse reflection surface.

[0025] The “L” value is an index of brightness. A larger “L” value indicates a brighter color. The “a” and “b” values are indexes of hue. The color varies toward red as the “a” value is increasing, while on the other hand the color varies toward green as the “a” value is decreasing. The color varies toward yellow as the “b” value is increasing, while on the other hand the color varies toward blue as the “b” value is decreasing.

[0026] According to the present invention, it is further preferable that the golf ball satisfies −14≦b≦−0 after subjecting the golf ball to a weathering test of irradiation for 120 hours using a Sunshine Weather meter. If the “b” value is more than 0, the yellow tone is getting intensive, thus whiteness is deteriorated. On the other hand, in order to control the “b” value less than −14, it is inevitable to control the initial “b” value less than −16, thus the initial color tone of the golf ball becomes too blue.

[0027] The above weathering test is a test which promotes the long-term-durability and is carried out using a Sunshine Weather meter according to JIS D 0205.

[0028] The “a” values of the one-piece golf ball at the initial state and after a weathering test are, but not limited to, preferably not less than −3.5, more preferably not less than −3.0, and preferably not more than 1.0, more preferably not more than 0.0. If the “a” value is less than −3.5, the green tone is too intensive. If the “a” value is more than 1.0, the red tone is too intensive. In both cases, the golf ball would give the subdued and heavy impression to the golfer.

[0029] According to the present invention, the golf ball retains the bright whiteness even after the weathering test as well as at the initial state by using 1 to 7 parts of titanium oxide and 0.05 to 0.2 part of the blue pigment with respect to 100 parts of the base rubber by mass.

[0030] White tone of the golf ball is evaluated with Wcie which means the index representing whiteness according to “ISO 105-J02”. Smaller value of Wcie means the lack of whiteness. Herein, Wcie is determined by a color difference meter named “CR-221” manufactured by MINOLTA CO. using tristimulus values X, Y and Z as follows. Equation of whiteness according to CIE•ISO:

Wcie=Y+800(X ₀ −x)+1700(Y ₀ −Y)

[0031] (where X₀, Y₀ are the color-coordinates of a perfect diffuse reflection surface by lighting D_(65.)X₀=0.3127, Y₀=0.3291).

[0032] In the present invention, Wcie is preferably not less than 75, more preferably not less than 80, most preferably not less than 90, extremely preferably not less than 93 in terms of the color tone of the golf ball after the weathering test of irradiation for 120 hours using a Sunshine Weather meter. If Wcie is less than 75, the golf ball becomes a dull white color, and thus the appearance is not good. Further, the upper limit of Wcie may be, but is not limited to, 145, preferably 135, more preferably 125, because of the limitation of the raw materials of the golf ball. The one-piece golf ball of the invention preferably has the initial Wcie of not less than 108, more preferably not less than 115, and preferably not more than 145, more preferably not more than 142, most preferably not more than 133. If the initial Wcie is less than 108, the sufficient whiteness is not retained after the weathering test as well as the initial white tone is lowered.

[0033] The rubber composition may further contain conventional fillers such as barium sulfate, calcium carbonate and zinc oxide, softening agent and antioxidant, in addition to the titanium oxide and the blue pigment. The base rubber, the pigments, the fillers, the co-crosslinking agents and the like may be mixed by a roll-kneader and pressure-molded in the heating condition to obtain a one-piece golf ball body. The one-piece golf ball body is coated with a clear paint to obtain the one-piece golf ball which comprises a clear paint film coating the golf ball body.

[0034] The clear paint is not limited, as long as it does not contain a pigment substantially. The clear paint includes, for example, a solvent-borne, aqueous, or water-dispersible form of urethane resin, epoxy resin, acrylic resin and the like. In view of the high durability against the deformation and the impact by shot and excellent coating-workability, the solvent-borne urethane resin is preferred. The clear paint film may further contain a fluorescent brightener, an ultraviolet adsorbent, a light stabilizer and the like in order to improve the visibility and the weather-resistance.

[0035] The fluorescent brightener is a substance which serves to enhance the whiteness, for example, whiteness of cloth, paper, or plastics, when added thereto and has a property of absorbing light in the ultraviolet region (330 to 380 nm) of the spectrum of sunlight while showing fluorescence of blue-violet light (400 to 450 nm) in the visible light range.

[0036] Examples of the fluorescent brightener are stilbene derivatives, styryl derivatives of benzene and biphenyl, bis(benzazol-2-yl) derivatives, derivatives of coumarin, carbostyryl, naphthalimide and dibenzothiophene-5,5-dioxide, pyrene derivatives, and pyridotriazole. Among them, derivatives of 4,4′-diaminostilbene-2,2′-disulfonic acid, 4-methyl-7-diethylaminocoumarin, 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene and the like are preferred.

[0037] Examples of the ultraviolet absorbers are salicylic acid derivatives, benzophenones, benzotriazoles, substituted acrylonitriles, and nickel complexes. An example of the light stabilizer is a hindered amine type light stabilizer.

[0038] There is no particular limitation to the method of applying the clear paint to the golf ball body. For example, a method such as spraying a solvent-borne clear paint onto the golf ball body with a spray gun may be employed.

[0039] The clear paint film coated has no limitation on its thickness, and preferably has the thickness of not less than 3 μm, and not more than 25 μm. If the thickness of the clear paint film is less than 3 μm, the gross of the resultant golf ball is lowered. If the thickness is more than 25 μm, the dimple does not work, thus the flying performance of the golf ball is lowered.

EXAMPLES

[0040] The following examples illustrate the present invention, however these examples are intended to illustrate the invention and are not to be construed to limit the scope of the invention. Many variations and modifications of such examples will exist without departing from the scope of the inventions. Such variations and modifications are intended to be within the scope of the invention.

[0041] [Evaluation Method]

[0042] (i) Initial Appearance

[0043] The initial appearance of the one-piece golf balls (after they were produced and before weathering test) were evaluated by 100 golfers.

[0044] Criteria:

[0045] Excellent: Number of the golfers who felt good about the appearance is more than or equal to 80.

[0046] Good: Number of the golfers who felt good about the appearance is between 51 and 79.

[0047] Poor: Number of the golfers who felt good about the appearance is less than or equal to 50.

[0048] (ii) Appearance after the Weathering Test

[0049] The one-piece golf balls were subjected to the weathering test using a Sunshine Super Long Life Weather meter available from Suga Test Instruments, based on the following conditions. The appearance of the golf ball after the weathering test was evaluated by 100 golfers.

[0050] Condition for the Weathering Test:

[0051] Chamber temperature 63° C., Humidity 50%, rainfall for 12 minutes of 60 minutes, and an irradiation for 120 hours.

[0052] Criteria:

[0053] Excellent: Number of the golfers who felt good about the appearance is more than or equal to 80.

[0054] Good: Number of the golfers who felt good about the appearance is between 51 and 79.

[0055] Poor: Number of the golfers who felt good about the appearance is less than or equal to 50.

[0056] [Durability Test]

[0057] The one-piece golf balls were crashed into the metal plate at the speed of 45 m/s using an air-gun, and times up to which the golf balls are cracked were measured. Each value obtained in terms of each golf ball was reduced to an index number relative to the measured value obtained in Example 1 being assumed 100 (The larger number indicates better durability).

[0058] [Production and Evaluation of the One-Piece Golf Balls]

[0059] Based on the formulation of table 1, the rubber composition was kneaded and pressure-molded at the temperature of 160° C. for 30 mins. to obtain one-piece golf ball bodies of examples 1 to 11 and comparative examples 1 to 5. The one-piece golf ball bodies were coated with the clear paint and dried to obtain one-piece golf balls coated with the clear paint film. The obtained golf balls were evaluated in terms of the initial appearance, the appearance after the weathering test, the durability and the like. The results were shown in table 1. TABLE 1 Examples 1 2 3 4 5 6 7 8 Golf ball compositions BR11 100 100 100 100 100 100 100 100 zinc oxide 23.5 23.5 23.5 23.5 23.5 23.5 23.5 23.5 methacrylic acid 24 24 24 24 24 24 24 24 dicumyl peroxide 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 titanium oxide 1 1 2 2 3 3 3 5 blue pigment 0.05 0.2 0.05 0.09 0.09 0.2 0.12 0.09 violet pigment — — — — — — — — Evaluation of initial state L value 89.7 84.1 89 87.1 87.6 84.3 86.6 88.9 a value −0.9 −0.8 −0.9 −0.8 −0.9 −0.8 −0.6 −0.9 b value −8.2 −13.2 −8.6 −12.2 −11.5 −15.5 −13.1 −10.8 Wcie 115 130 115 130 127 142 133 126 appearance E E E E E G E E Evaluation after weathering test L value 87.3 83.1 87.7 86.1 85.9 82.5 85 87.3 a value −2.6 −2.6 −2.7 −2.7 −2.6 −2.6 −2.5 −2.8 b value −1.8 −6.0 −2.0 −10.7 −5.5 −8.7 −6.5 −4.8 Wcie 80 93.0 81.0 121 95 106 99 94 appearance G E G E E E E E Durability 100 100 98 97 95 95 96 94 Comparative Examples 9 10 11 1 2 3 4 5 Golf ball compositions BR11 100 100 100 100 100 100 100 100 zinc oxide 23.5 23.5 23.5 23.5 23.5 23.5 23.5 23.5 methacrylic acid 24 24 24 24 24 24 24 24 dicumyl peroxide 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 titanium oxide 5 7 7 1 1 9 9 5 blue pigment 0.2 0.05 0.2 0.03 0.22 0.03 0.1 0.02 violet pigment — — — — — — — 0.02 Evaluation of initial state L value 84.7 91.3 85.6 89 82.9 93.8 87.2 89.4 a value −0.8 −0.9 −0.8 −0.9 −0.8 −0.9 −1 0.1 b value −13.4 −8.1 −9.6 −6.5 −18.3 −5.1 −12.6 −6.7 Wcie 132 117 115 105 154 108 132 107 appearance E E E P P G E P Evaluation after weathering test L value 82.9 89.7 83.7 88.2 81.2 89.9 85.7 87.6 a value −2.6 −2.7 −2.8 −2.6 −2.5. −2.8 −2.6 −1.7 b value −7.3 −2.1 −3.8 0.9 −12.1 1.2 −10.2 0.4 Wcie 99 86 83 68 122 70 118 69 appearance E G G P E P E P Durability 93 93 93 100 100 82 75 94

[0060] As was shown in table 1, the golf ball of the present invention had bright whiteness and excellent appearance where the initial b value is from −15.5 to −8.1 and the initial Wcie is from 115 to 142. Further, the b value and Wcie after the weathering test were −10.7 to −2.0 and 80 to 106, respectively. The golf balls after the weathering test were white without being tinged with yellow. This result indicated that the golf ball of the present invention is excellent in long term-weather resistance.

[0061] Comparative example 1 was the case where the titanium oxide content was 1 mass part and the blue pigment content was as low as 0.03 mass part. In this case, since the titanium oxide content and the blue pigment content were low, the golf ball which gave the transparent impression was obtained, and thus the initial appearance was deteriorated. Further, the initial b value was as large as −6.5, thus the golf ball had b value of 0.9 and was tinged with yellow after the weathering test. Furthermore, the initial Wcie was 105, and the initial white tone of the golf ball appearance was lowered. In addition, the weathering test further lowered Wcie to 68, and thus the white tone of the golf ball appearance was further deteriorated.

[0062] Comparative example 2 was the case where the titanium oxide content was 1 mass part and the blue pigment content was as large as 0.22 mass part. Since the golf ball of the comparative example 2 had too small initial b value of −18.3, the golf ball had an appearance tinged with blue, resulting in the deterioration of the white tone.

[0063] The golf ball of comparative example 3 was the case where the amount of the blue pigment are low, thus the initial b value was as large as −5.1. The weathering test increased b value of the golf ball to 1.2 and tinged the golf ball with yellow. In addition, Wcie value of 70 after the weathering test indicated that the initial white tone of the appearance was also deteriorated. The durability of the golf ball was also deteriorated, because the titanium oxide content was as large as 9 mass parts.

[0064] The golf ball of the comparative example 4 had no problem of the color tone of the appearance, however, the durability of the golf ball was deteriorated, because the titanium oxide content was as large as 9 mass parts.

[0065] Comparative example 5 was the case where the violet pigment was used in combination of titanium oxide and blue pigment as a component serving as a pigment. In the above case, the initial Wcie of 107 indicated that the initial white tone was deteriorated. In addition, Wcie of 69 after the weathering test indicated that the initial white tone of the appearance was further deteriorated. This result also indicated that use of the violet pigment did not provide the golf ball which has the bright whiteness as described and aimed in the present invention.

[0066] The present invention is configured as described above and provides the one-piece golf ball which has an excellent durability, because it contains 1 to 7 mass parts of titanium oxide with respect to 100 parts of the base rubber. Further, use of the blue pigment in an amount of 0.05 to 0.2 mass part in combination of the titanium oxide imparts the bright whiteness to the golf ball and makes the golf ball retain the white appearance even when the clear paint film and the rubber composition constituting the golf ball body were deteriorated and yellowed. This application is based on Japanese Patent application No.2,001-136,519 filed on May 7, 2001, the contents of which are hereby incorporated by reference. 

1. A one-piece golf ball comprising a golf ball body obtained by vulcanizing a rubber composition; and a clear paint film coating the golf ball body, wherein a component serving as a pigment of the rubber composition consists of 1 to 7 parts of titanium oxide; and 0.05 to 0.2 part of a blue pigment with respect to 100 parts of a base rubber by mass(weight).
 2. The one-piece golf ball according to claim 1, wherein the titanium oxide is present in the rubber composition in an amount of 2 to 5 parts with respect to 100 parts of the base rubber by mass.
 3. The one-piece golf ball according to claim 1, wherein the blue pigment is present in the rubber composition in an amount of 0.10 to 0.15 part with respect to 100 parts of the base rubber by mass.
 4. The one-piece golf ball according to claim 1, wherein an appearance of the golf ball has the color tone which satisfies the following relationships specified by Lab color specification in terms of initial b value: −16≦b≦−8.
 5. The one-piece golf ball according to claim 4, wherein an appearance of the golf ball has the color tone which satisfies the following relationships specified by Lab color specification in terms of initial b value: −14≦b≦0 after subjecting the golf ball to a weathering test of irradiation for 120 hours using a Sunshine Weather meter.
 6. The one-piece golf ball according to claim 1, wherein an appearance of the golf ball has the color tone which satisfies the following relationships specified by ISO 105-J02 in terms of Wcie: Wcie≧75 after subjecting the golf ball to a weathering test of irradiation for 120 hours using a Sunshine Weather meter.
 7. The one-piece golf ball according to claim 4, wherein an appearance of the golf ball has the color tone which satisfies the following relationships specified by ISO 105-J02 in terms of Wcie: Wcie≧75 after subjecting the golf ball to a weathering test of irradiation for 120 hours using a Sunshine Weather meter.
 8. The one-piece golf ball according to claim 7, wherein the appearance of the golf ball has the color tone which satisfies the following relationships in terms of Wcie: 125≧Wcie≧93 after subjecting the golf ball to the weathering test of irradiation for 120 hours using a Sunshine Weather meter. 